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An EKG evaluates and records the electrical activity of the heartbeat.

An EKG is a machine that monitors the heart's functions. [©Shutterstock, 2010]
©Shutterstock, 2010
An EKG is a machine that monitors the heart's functions.

The American Heart Association describes an electrocardiogram, also referred to as an EKG or an ECG, as a test which evaluates and records the electrical activity of the heart beat. Occasionally, the EKG is referred to as the 12-lead EKG or 12-lead ECG, because results are simultaneously read from 12 different places on the body. Doctors use EKGs as a diagnostic tool, a method for detecting damage after trauma to the heart or a method for monitoring the effectiveness of treatment. Even though the EKG is a relatively simple test, it provides valuable diagnostic information to doctors.

How the EKG Works

To thoroughly understand how an EKG works, it is necessary to understand the basic functioning of the heart. Each time the heart beats, an electrical impulse starting in the right atrium of the heart causes the right and left atria to contract. Next, the impulse travels through several pathways before stimulating the lower chambers of the heart, also known as the right and left ventricles. On the EKG, the first wave or "P wave" indicates the contraction of the right and left atria. The next wave, or "QRS complex," indicates that the ventricles are contracting. Following the "QRS complex" there is the "ST segment" which shows the time lapse from the end of ventricle contraction to the start of the ventricle resting phase. The ventricle resting phase is indicated by the "T wave."

Uses of an EKG

The Stanford Hospital and Clinics cite several common reasons for ordering an EKG, such as identifying the cause of chest pain, irregular heart beats, dizziness, fatigue, shortness of breath or fainting. A doctor may order an EKG in advance of a surgical procedure if there is concern about the patient's heart function. Some medical professionals use EKG results to check the status of the heart after a heart attack, a bout with endocarditis or surgical procedures involving the heart. Furthermore, an EKG may be a valuable tool when monitoring the effectiveness of a pacemaker or certain heart medications. Additionally, some doctors order EKGs to establish baseline heart function, which can be compared with future EKGs to determine if any significant changes have occurred.

Preparing for an EKG

Generally, it is not necessary to do anything specific to prepare for an EKG, however, some medical professionals recommend limiting vigorous exercise and cold water consumption prior to an EKG. It is thought that cold water may actually change the electrical patterns during an EKG, resulting in an inaccurate test. Vigorous physical activity may increase the heart rate, possibly reducing the validity of the test. Also, patients should leave jewelry at home or in a safe place during the procedure; such items could interfere with the results. Finally, patients should inform the doctor or technician of any changes in medication regime. This includes prescribed medications, over-the-counter medications and herbal medications.

What to Expect During an EKG

Prior to the procedure, the patient undresses above the waist. Typically, the patient receives a gown to maintain patient privacy and dignity. Next, the patient is asked to lie on the examining table. The National Heart, Lung, and Blood Institute notes that the first major step in the EKG procedure involves placement of electrodes, which are sticky, quarter-sized patches, on the skin of the patient's chest, arms and legs. Occasionally, it's necessary to shave the area before placement of electrodes, so that they stick to the skin. Once all electrodes are placed, the patient remains motionless on the table as the machine records the heart's electrical signals. In order to obtain accurate results, it is imperative that the patient minimizes movements and refrains from talking while the EKG machine records the results onto graph paper. Sometimes, the patient can see the results on a screen. Generally, the entire procedure takes only 10 minutes. Once the procedure is complete, the technician removes the electrodes or sticky patches and the patient can resume normal activities.

EKG Side Effects

The Mayo Clinic notes that an EKG is a relatively safe procedure. The only uncomfortable part of the procedure may occur when the technician removes the electrodes. Some patients compare the electrode removal to taking off an adhesive bandage, except the sticky material on the electrode is sometimes more difficult to remove. Occasionally, a patient develops a mild rash in the area where the electrodes were attached. Fortunately, this rash or area of redness generally dissipates without treatment.

Factors That May Interfere With an EKG

Before having an EKG, the doctor or technician may ask the patient certain questions to identify factors that may interfere with the EKG procedure or results. Conditions or factors that can interfere with the EKG include fluid in the abdomen, pregnancy, obesity, certain medications, electrolyte abnormalities, chest size, location of heart, smoking, exercise and recent consumption of high carbohydrate meals.

What an EKG Shows

The EKG can show a variety of different problems. Specifically, the EKG can identify the presence of an ongoing or previous heart attack in a patient. Other conditions detected by an EKG include minimal to no blood flow to the heart muscle, irregular heart rhythm, heart failure, heart valve disease, congenital heart defects, an enlarged heart or thickened heart muscle, pericarditis, heart block or long QT syndrome.

Specific Types of EKG Monitors

When the doctor suspects that a heart problem is inconsistent, presenting only under certain circumstances, such as physical exertion, a specific type of EKG may be used. During an EKG stress test, the patient exercises while electrodes evaluate the electrical activity of the heart. The Holter or event monitor is similar to the standard EKG; however, it is a portable device, worn while the patient engages in typical daily activities. The benefit is that it takes readings for an extended period of time as opposed to a few minutes.

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